How Does Weight Affect Immunity?

At risk populations are more at danger if they contract an illness like influenza, pneumonia or COVID-19. Here in America one of our biggest at-risk populations is people who are overweight or obese, as an estimated 34% of Americans are obese according to the last National Health and Nutrition Examination Survey (NHANES). (1) There are a couple different reasons as to why overweight/obese patients are more of a concern in relation to COVID-19; they are more susceptible to getting the disease, they have the disease for longer, and they have a worse clinical outcome. (2) To start it’s important to understand what qualifies as overweight or obese. The National Institutes of Health (NIH) define overweight as a BMI (weight in kilograms divided by height in meters squared) of 25-29.9 kg/m2 and obese as a BMI greater than 30 kg/m2. (3) BMI isn’t an end all measure though and should just be a guideline; it’s important to also take into consideration body composition, activity level, sport etc.)


So why are people who are overweight/obese more likely to get a disease like COVID-19? One reason is physical inactivity. Individuals who don’t participate in any sort of physical activity are more likely to be overweight/obese and this reduced physical activity level impairs the immune response. A 2015 study comparing blood immune markers in sedentary individuals versus those who regularly exercise found that regular exercise enhanced the response of the immune system when a pathogen was present and being sedentary for long periods of time reduced the response of the immune system. (4) This population also has higher leptin (pro-inflammatory) and lower adiponectin (anti-inflammatory) cells. (2) This means that overall their bodies are in an inflammatory state. So, when a pathogen is present this inflammation causes a reduced immune system response leading to an overall delay in the resolution of the infection. Because of this, this population will suffer from the disease for longer than someone who wasn’t overweight/obese. In the case of COVID-19 the disease ends up affecting our lungs, leading to the air sacs in the lungs swelling and filling with fluid. This makes it hard to breath and in the worse cases leads to having to be put on a machine that breathes for you (intubation). Many overweight/obese people have respiratory problems, whether that’s sleep apnea or getting winded easily. The cause of this is somewhat still unknown but a recent research study in mice has shown that the motion of the diaphragm, the muscle that contracts to fill the lungs with air, was significantly decreased in overweight/obese mice. (5) This means that the mice weren’t getting as much air into their lungs with each breath, so if they were to exert themselves, even from walking on a treadmill, they would be out of breath. If a person who has this decreased diaphragm motion contracts COVID-19 then their impaired lungs would become even more impaired. This, along with the chronic inflammatory state their immune cells are fighting against, will cause them to have worse clinical outcomes meaning a higher change of needing to be intubated and longer stays in the ICU.


As with most things more research is needed in this area to fully understand the risk overweight/obese people are at for contracting diseases like COVID-19 and how the disease will affect them in the long term. For now though, those who are overweight/obese need to be more cautious when it comes to staying healthy. This means washing your hands more, starting to or continuing to exercise regularly and staying away from those who are sick.


REFERENCES


1. Caspard H, Jabbour S, Hammar N, et al. Recent trends in the prevalence of type 2 diabetes and the association with abdominal obesity lead to growing health disparities in the USA: an analysis of the NHANES surveys from 1999 to 2014. Diabetes Obes Metab. 2018;20(3):667-671. doi: 10.1111/dom.13143

2. Luzi L, Radaelli MG. Influenza an dobesity: its odd relationship and the lessons for COVID-19 pandemic. Acta Diabetol. 2020;57:759-764. https://doi.org/10.1007/s00592-020-01522-8

3. https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm

4. Zheng Q, Cui G, Chen J, et al. Regular exercise enhances the immune response against microbial antigens through up-regulation of toll-like receptor signaling pathways. Cell Physiol Biochem. 2015;37:735-746. Doi: 10.1159/000430391 https://www.karger.com/Article/Pdf/430391

5. Buras ED, Converso-Baron K, Davis CS, et al. Fibro-adipogenic remodeling of the diaphragm in obesity associated respiratory dysfunction. Diabetes. 2019;68(1):45-56. https://doi.org/10.2337/db18-0209

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